In connection with the present invention, the term “steering wheel” is used synonymously with every type of steering mechanism. Thus control sticks, such as are known, for example, in airplanes, also fall under the concept of a steering wheel in the meaning of the present invention.
As the tracking of a vehicle becomes increasingly automated, it is necessary to determine whether the driver of the vehicle is carrying out his tasks or not. Thus, it has long been known, for example, from the railroad industry, using a so-called “dead man” switch, to check at regular intervals whether the train driver is awake or not. From the area of motor vehicles, devices and methods are also known to regularly test the reaction speed and therefore the wakefulness of the driver. From German Published Patent Application No. 195 18 914, a device is known for testing the alertness and reactions of an automobile driver, which generates a signal that must be acknowledged by a finger pressure of the driver on the steering wheel. The time duration from the occurrence of the signal to its acknowledgment is used as a measure for the reactivity and alertness of the driver.
In the driver-assistance systems installed at least in future vehicles, for example, tracking support or lateral wind compensation are to be provided. These functions can tempt the driver to take his or her hands from the steering wheel while driving. For this situation, driver-assistance systems are not provided. Rather, the driver should always have control over the vehicle and should only be supported in a supplemental fashion by the driver-assistance systems. To assure this division of labor between driver and driver-assistance system, the contact of the hands of the driver on the steering wheel of the vehicle is continuously monitored.
The present invention is based on the objective of furnishing a method and device for detecting the contact of hands on a steering wheel, which is easy to assemble and which operates reliably over the entire service life of the vehicle.
This objective is achieved according to the present invention by a method for detecting the contact between hands and a steering wheel, in which a first signal having a first frequency is generated, the first frequency being a function of whether the hands of the vehicle driver are in contact with the steering wheel or not, a second signal having a second frequency being generated, and an output signal being generated as a function of the frequencies of the first and the second signal.